1. Field of the Invention
The invention relates to an ablation catheter arrangement for high-frequency ablation of tissue, in particular for targeted creation of linear and/or spot lesions in coronary tissue.
2. Description of the Related Art
Heart disease is widespread. The most common diseases affecting the myocardium but not the coronary vessels involve the conduction of stimuli. With normal stimulus conduction, these electric stimuli are formed by the sinus node, which is situated in or on the right auricle of the heart, and propagate over the entire myocardium by way of the AV node (atrioventricular node), the His bundle, the Tawara branch and the Purkinje fibers, to thereby induce contraction of the heart from the apex of the heart and proceeding to the atria by way of the myocardium of the two ventricles. This results in a circulation path.
Interference-free stimulus conduction then leads to the physiologically trouble-free ejection of blood into the pulmonary artery and aorta. The structure of the coronary tissue, which behaves like a muscle that can be stimulated equally at all points and in all directions, is noteworthy. In a healthy heart, after successful activation of the ventricular musculature, stimulus conduction is blocked by equal polarization of all muscular cells, so that no potential difference is capable of enabling electric stimulus conduction. This condition is known as the refractory time because all the muscle cells are refractory and cannot be stimulated. This condition dissipates on its own after a short period of time to allow the next stimulus and thus the next heartbeat.
If there is an anatomical or functional obstacle—for example, in a bundle of branching Purkinje fibers, then a dangerous intermediate stage may occur before the conduction is completely blocked at this point: a unidirectional block. The damaged area here retards the passage of a stimulus until at some point it becomes refractory with respect to the next stimulus, i.e., this area is difficult or impossible to stimulate. However, this stimulation can pass through the damaged area in the opposite direction because it reaches this damaged area at a later point in time, at which it may no longer be refractory. The transit time delay occurs due to the “detour” by which the stimulus must travel.
If the remaining refractory path behind this stimulus, which is now running in the opposite direction (technical term: retrograde conduction), is shorter than the circulation path, the stimulus does not die out within the circulation path and can run through it continuously. In this case we speak of a circulating stimulus.
The risk here is of reentry of the stimulus wave into the surrounding tissue when the latter is no longer refractory. A stimulus that would otherwise be self-sustaining, so to speak, may develop. This is the cause of serious tachycardiac arrhythmias associated with the risk of fibrillation.
In addition to medication therapies, electrophysiological therapy has become successful here. Certain spots on the myocardium are heated by high frequency in a targeted manner and are thereby ablated to prevent the electrical conduction. Ablated tissue is no longer conductive.
Ablation catheter arrangements are used for ablation therapy.
As indicated by the name, these include an ablation catheter and an ablation generator plus a coolant pump.
The ablation catheter is an elongated catheter which is guided through a blood vessel to the treatment site. It includes an electrically insulating tubular sheath and electrically conductive feeder lines and coolant flow paths running inside the sheathing. On the distal end there are electrode poles suitable for delivering high-frequency energy pulses. The electrode poles are pointed or flat and are electrically connected to the feeder lines. In addition, an ablation catheter may contain control means with which the distal catheter section can be brought into a linear or circular form, for example. Linear lesions or circular lesions can thus be created around the mouth of the pulmonary veins, for example.
At the output end, the ablation generator generates a high-frequency energy pulse signal or a high-frequency energy field, which is sent to the feeder lines of the ablation catheter and is sent from there to the electrode poles for delivery to the coronary tissue. The generator is controlled by an operator. A device for cooling ablation catheters which supplies a liquid cooling medium (usually a physiological saline solution) in the at least one coolant path of the ablation catheter on demand by the operator, whereby the coolant leads through the coolant path up to the electrode poles on the distal section or on the distal end. The catheter and the ablation site are therefore both cooled by circulating the coolant through the catheter either through another coolant path and/or by guiding the coolant to the ablation site through openings in the distal section. The cooling device also has a controller which controls the pump, so that it generates at least one lower flow rate and one elevated flow rate. In this way, the cooling device ensures a uniform and constant flow of coolant through the catheter to the electrode poles at a low flow rate. If the operator prompts the delivery of a high-frequency signal, increased delivery of coolant is required. The operator makes this demand by creating an increased flow rate in the cooling device by means of a foot pedal simultaneously with the control of the ablation generator. This produces an even greater cooling.
One disadvantage of this manual control is that the operator must operate two different systems. This operation alone requires so much concentration and training that there may easily be mistakes in guidance of the catheter. Even if the control of the cooling device is performed by an assistant, coordination of the operation of the catheter, the ablation generator and the pump requires a great deal of concentration and coordination.
Known further developments include ablation arrangements constructed so that the generator and a specific cooling device which is compatible with the generator cooperate. These arrangements are always coordinated with one another in such a way that replacement of the generator involves replacement of the cooling device at the same time. On delivery of a high-frequency pulse, the generator switches the flow rate of the pump to an increased coolant flow. The pulse and the coolant are fed into the catheter via a proprietary interface between the catheter on the one hand and the generator and the pump on the other hand. It is thus a disadvantage that the operator is limited to precisely such a pair of devices, i.e., the ablation generator and the pump.
An individual adjustment, which is sometimes also based on the indication and the type of catheter associated with it or the required energy output is thus impossible. It may thus be necessary during a treatment to change to another ablation generator while retaining the cooling device and the constant cooling with the low coolant flow and the increased coolant flow, e.g., because a higher ablation energy is required, an incompatible ablation catheter must be used, or because the ablation generator is defective. With the ablation arrangements known in the past, the user loses the automatic coupling of the cooling device to the ablation generator because the pump cooperates only with the compatible generator. Cooling of the catheter must thus be interrupted or, as described above, controlled manually. The interruption in cooling may be very painful for the patient due to the catheter heating up again and may also lead to a loss of volume of the catheter tubing because the volume of the cooling liquid is maintained. Under certain conditions, the loss of catheter cooling may also be a risk to the patient. Manual control has the disadvantages described above.